It is known to support a surface, such as may be defined by a keyboard supporting tray, for vertically swinging movement relative to a base, such as may be defined by the top of a table or work station, by a mechanism including a pair of link elements each having first and second ends thereof pivotally connected to a surface mounting element and a base mounting element, respectively. Such mechanisms typically include a counterbalance spring tending to bias the surface mounting element and link elements upwardly relative to the base, and a manually operable locking mechanism serving to releasably retain the surface mounting element in a desired vertical position.
It has also been proposed to provide an additional bracket serving to interconnect the surface mounting element to the link elements in a manner allowing downwardly directed tilting movement of the surface mounting element in combination with an additional manually operable locking mechanism serving to releasably retain the surface mounting element in a desired tilted position.
Known clamping mechanisms are disclosed for example by U.S. Pat. Nos. 4,616,798; 4,644,875; 4,691,888; 5,037,054 and 5,791,263.